Sodium acetate

Sodium acetate, (also rarely, sodium ethanoate) is the sodium salt of acetic acid. It is an inexpensive chemical produced in industrial quantities for a wide range of uses.

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Applications

Sodium acetate is used in the textile industry to neutralize sulfuric acid waste streams, and as a photoresist while using aniline dyes. It is also a pickling agent in chrome tanning, and it helps to retard vulcanization of chloroprene in synthetic rubber production.

Sodium acetate is the chemical that gives salt and vinegar chips their flavour. It may also be added to foods as a preservative; in this application it is usually written as "sodium diacetate" and labeled E262.

As the conjugate base of a weak acid, a solution of sodium acetate and acetic acid can act as a buffer to keep a relatively constant pH. This is useful especially in biochemical applications where reactions are pH dependent.

Sodium acetate is also used in consumer heating pads or hand warmers and is also used in "hot ice". When sodium acetate trihydrate crystals (melting point 58 °C) are heated to around 100 °C, they melt. When this melt cools, it gives a supersaturated solution of sodium acetate in water. This solution is capable of supercooling to room temperature, well below its melting point, without forming crystals. By clicking on a metal disc in the heating pad, a nucleation center is formed which causes the solution to crystallize into solid sodium acetate trihydrate again. The bond-forming process of crystallization is exothermic, hence heat is emitted.^[1][2][3] The latent heat of fusion is about 264–289 kJ/kg.^[4]

Preparation

Sodium acetate is inexpensive, and is usually purchased from chemical suppliers, instead of being synthesized in the laboratory. It is sometimes produced in a laboratory experiment by the reaction of acetic acid with sodium carbonate, sodium bicarbonate, or sodium hydroxide. These reactions produce sodium acetate(aq), water, and carbon dioxide which leaves the reaction vessel as a gas.

CH₃–COOH + Na⁺[HCO₃]^– → CH₃–COO^– Na⁺ + H₂O + CO₂

This is the well-known "fizzing" reaction between baking soda and vinegar. 84 grams of sodium bicarbonate react with 750 g of 8% vinegar to make 82 g sodium acetate in water. By subsequently boiling off most of the water, one can refine either a concentrated solution of sodium acetate or actual crystals.

Reactions

Sodium acetate can be used to form an ester with an alkyl halide such as bromoethane:

H₃C–COO^– Na⁺ + Br–CH₂–CH₃ → H₃C–COO–CH₂–CH₃ + NaBr

Gallery

References

1. ^ Crystallization of Supersaturated Sodium Acetate. Journal of Chemical Education.
2. ^ "Fake" latent heat and supersaturation
3. ^ How do sodium acetate heat pads work?. HowStuffWorks. Retrieved on 2007-09-03.
4. ^ Thermal Energy Storage: Systems and Applications, By Ibrahim Dincer, Marc A. Rosen, p. 155 [1]